Preheat your oven to 350°F (175°C) and lightly grease a baking dish (approximately 9x9 inches) with melted coconut oil.
In a large bowl, mix together the rolled oats, diced apples, almond milk, maple syrup, vanilla extract, cinnamon, nutmeg, baking powder, and salt. Stir until all ingredients are well combined.
If using, fold in the chopped walnuts or pecans for extra crunch.
Pour the mixture into the prepared baking dish and spread it evenly.
Sprinkle the brown sugar evenly over the top for a caramelized finish.
Bake in the preheated oven for 30-35 minutes, or until the edges are golden and the center is set—a toothpick inserted should come out clean.
Remove from the oven and let it cool for about 10 minutes before slicing.
Notes
Serve warm, topped with yogurt or ice cream, and garnish with cinnamon and apple slices.